1. Field of the Invention
The present invention relates to a chain wildcat for an anchor handling winch, and more specifically it relates to a chain wildcat, preferably for removable attachment to an end of a drive shaft in an anchor handling winch for adapting the anchor handling winch to chain of different dimensions. The invention further relates to an anchor handling winch equipped with a chain wildcat.
2. Description of the Related Art
Put briefly, a wildcat is the drum or wheel that heaves in the chain, where the drum or wheel is advantageously provided with at least five pockets that engage the chain links. Different chain dimensions therefore require the use of different-size pockets.
The international standard ISO 7365 relating to winches for towing and anchor handling vessels refers to emergency release in general without distinguishing between wires and chain, and is therefore regarded as unsuitable or insufficient as regards anchor handling winches equipped with both wire drum and chain wildcat. For a wire drum, it is a requirement that the drum can be placed in neutral within a maximum number of seconds, but for a chain wildcat there is at present so such requirement.
Inadequate requirements for placing a chain wildcat in neutral lead to a risk of an anchor handling vessel foundering, especially when working against the towline, because many anchor handling vessels in that situation have sufficient transverse force to capsize the vessel. This problem is described in more detail by the English textbook author on ship stability, Ian Clark.
On previously known anchor handling winches, the wildcat is typically loose, and is attached to the end of a drive shaft which often has a pentagonal, key or spline connection. The said winches further typically consist of a drive unit which drives the drive shaft, where a disengageable wire drum is connected to the drive shaft, and also where different removable wildcats can be mounted to the end of the drive shaft equipped with a journal so as to enable the vessel to handle several different chain dimensions.
Other systems are previously known where the whole of the drive shaft is disengageable in relation to the drive unit, but as far as the applicant is aware none are known where the wildcat itself can be disengaged from the drive shaft, in an emergency release, for example, to prevent the vessel from capsizing.